|Número de publicación||US7091654 B2|
|Tipo de publicación||Concesión|
|Número de solicitud||US 09/939,848|
|Fecha de publicación||15 Ago 2006|
|Fecha de presentación||27 Ago 2001|
|Fecha de prioridad||26 Abr 2000|
|También publicado como||US6387717, US6713312, US20020000548, US20020127750, US20060267472|
|Número de publicación||09939848, 939848, US 7091654 B2, US 7091654B2, US-B2-7091654, US7091654 B2, US7091654B2|
|Inventores||Guy T. Blalock, Sanh D. Tang, Zhaohui Huang|
|Cesionario original||Micron Technology, Inc.|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citas de patentes (22), Citada por (3), Clasificaciones (14), Eventos legales (3)|
|Enlaces externos: USPTO, Cesión de USPTO, Espacenet|
This application is a divisional of application Ser. No. 09/559,153, filed Apr. 26, 2000, now U.S. Pat. No. 6,387,717, issued May 14, 2002.
1. Field of the Invention
The present invention relates to field emitters and methods of fabricating the same. More particularly, the present invention relates to forming field emission tips by the use of facet etching.
2. State of the Art
Various types of field emitters are used in a variety of devices, from electron microscopes to ion guns. However, one of the most prevalent commercial applications of field emitters is flat panel displays, such as cold cathode field emission displays (“FEDs”) used for portable computers and other lightweight, portable information display devices.
As illustrated in
Other field emission tip formation techniques which do not involve isotropic etching are also known. For example, U.S. Pat. No. 5,312,514, issued May 17, 1994 to Kumar (“the Kumar patent”), relates to forming field emission tips by distributing a discontinuous etch mask material across an electrically conductive material layer. The discontinuity of the etch mask material forms random openings therein. The etch mask material is selected such that the electrically conductive material layer will etch at a faster rate than the etch mask material (at least twice the rate) when the electrically conductive material layer is ion etched. The ion etch is performed until all of the etch mask is removed, which results in v-shaped valleys in the electrically conductive material defining peaked field emission tips therebetween. Further, the Kumar patent discusses using a low work function material for the electrically conductive material layer and also discusses depositing a low work function material over the electrically conductive material after the formation of the field emission tips. Although the method taught in the Kumar patent eliminates the use of an isotropic etch to form field emission tips, it lacks control over the field emission tip distribution and dimensions. The discontinuous layer of etch mask material results in a nonuniform distribution of field emission tips, since the positions of the openings in the discontinuous layer cannot be controlled. Furthermore, the discontinuous layer of etch mask material results in non-uniform dimensions between the field emission tips, since the thickness difference across the discontinuous layer cannot be controlled. In other words, the field emission tips formed in areas where less etch mask material existed over the conductive material will be shorter than in other areas. Moreover, since the etch mask material is a discontinuous layer rather than a patterned mask, the size or diameter of the field emission tips formed cannot be controlled.
Thus, it can be appreciated that it would be advantageous to develop a technique which would result in novel field emission tips having uniform distribution and uniform, precise dimensions.
The present invention relates to field emitters and methods of fabricating the same, wherein the field emission tips of the field emitters are formed by utilization of a facet etch.
In an exemplary method of the present invention, an etch mask is patterned on a conductive substrate material in the locations desired for subsequently formed field emission tips. The etch mask can be patterned in various shapes in order to achieve a desired field emission tip structure. For example, a circular mask element will result in a conical field emission tip, a triangular mask element will result in a tetrahedral field emission tip, a square mask element will result in a pyramidal field emission tip, and so on. The conductive substrate material is anisotropically etched to translate the shape of the mask into the underlying conductive substrate material, which forms a vertical column having a cross-section with the same shape as the mask element, from the conductive substrate material. The anisotropic etch is conducted for a predetermined duration of time, which will result in a column of a specific height required for the subsequently formed field emission tip. The etch mask element is then removed (optional) and the vertical column is facet etched to form the field emission tip.
The facet etching is generally performed in a chamber in which ions can be accelerated to strike a substrate, such as reactive ion etchers, magnetically enhanced reactive ion etchers, low pressure sputter etchers, and high density source etchers. As opposed to anisotropic etches, such as ion etching or plasma etching processes, in which ions strike the surface of the substrate substantially perpendicular to result in a vertical etch, a facet etch results in ions dispersed in a fashion which results in the ions striking 90 degree features (i.e., corners) of structures on the substrate at a rate which is about four to five times that of the rate at which ions strike substantially planar surfaces (e.g., surfaces laying substantially perpendicular to the ion emission source) on the substrate. In fact, with facet etching, the planar surfaces experience very little substrate loss. The facet etch creates a gradual slope of about 45 degrees at the corners of the structures on the substrate.
The facet etch is preferably performed in a reactive ion etcher wherein the substrate is placed on a cathode within a high-vacuum chamber into which etchant gases are introduced in a controlled manner. A radio frequency power source creates a plasma condition in the high-vacuum chamber which generates ions. The walls of the high-vacuum chamber are grounded to allow for a return radio frequency path. Due to the physics of the radio frequency powered electrodes, a direct current self-bias voltage condition is created at the substrate location on the cathode, which causes the generated ions in the plasma to accelerate toward and strike the substrate. The etchant gases utilized in the facet etch are preferably inert gases, including, but not limited to, helium, argon, krypton, and xenon. These inert gases have been found to enhance the uniformity of the facet etch process. It is, of course, understood that any other suitable gas or mixture of gases which are inert with respect to the material of the substrate may also be used.
Thus, the present invention eliminates the use of isotropic etching to form field emission tips and, thereby, eliminates the problems associated with isotropic etching. Although the present invention requires more steps than the typical isotropic etching technique of forming field emission tips, the methods of the present invention result in more uniform distribution, size, and height for the field emission tips, since the location and size of the etch mask elements defining the tip locations, as well as the depth of the anisotropic etch, can be precisely controlled. This precise control results in a field emission tip array having regular uniform tip spacing as well as precise, uniform tip height, thus improving the performance and reliability of the field emission display device formed therefrom. Furthermore, the precise control of the tip spacing allows the tips to be packed closer to one another, which results in a higher fidelity screen with more pixels per square inch.
The present invention also allows for low work function materials to be easily incorporated into the field emission tips. The overall work function of a field emission tip affects its ability to effectively emit electrons. The term “work function” relates to the voltage (or energy) required to extract or emit electrons from a field emission tip. The lower the work function, the lower the voltage required to produce a particular amount of electron emission. Thus, the incorporation of low work function materials in field emission tips can substantially improve their performance for a given voltage draw.
A variety of low work function materials can be incorporated into the field emission tips of the present invention. Such low work function materials include, but are not limited to, AlTiSix (aluminum titanium silicide [wherein x is generally between 1 and 4]), TiSixN (titanium silicide nitride), TiN (titanium nitride), Cr3Si (tri-chromium mono-silicon), TaN (tantalum-nitride), or the like. Moreover, other low work function materials, such as metals including cesium (Ce), and cermets including Cr3Si—SiO2 (tri-chromium mono-silicon silicon-dioxide), Cr3Si—MgO (tri-chromium mono-silicon magnesium-oxide), Au-SiO2 (gold silicon-dioxide), and Au—MgO (gold magnesium oxide), may also be used.
One embodiment of the invention for incorporating low work function materials into the field emission tips according to the present invention involves depositing a low work function material on a conductive substrate material. The low work function material may be deposited by ion beam sputtering, laser deposition, evaporation, chemical vapor deposition (CVD), and sputtering. An etch mask is then patterned on the low work function material to form discrete mask elements in the locations desired for the field emission tips to be formed. The low work function material and conductive substrate material are then anisotropically etched to form a column under each etch mask element from the conductive substrate material and a portion of the low work function material. The etch mask elements are then removed (optional). The vertical columns, capped with the low work function material, are then facet etched to form an array of low work function material-tipped field emission tips. Redeposition material, comprising a mixture of material from the vertical column substrate material and the low work function material, generated by the facet etch collects in corners at junctions of the vertical columns and the base conductive substrate during the facet etch.
Another embodiment of the invention for incorporating low work function materials into the field emission tips according to the present invention involves incorporating a sacrificial layer to assist the removal of redeposition material from the field emission tip. As with the previously discussed embodiments of the present invention, a low work function material is deposited on a conductive substrate material. An etch mask is patterned to form etch mask elements on the low work function material in the locations desired for the field emission tips to be formed. The low work function material and conductive substrate material are then anisotropically etched under such mask elements to form vertical columns from the conductive substrate material capped by a portion of the low work function material. The etch mask elements are then removed (optional). A sacrificial material, such as silicon dioxide or tetraethyl orthosilicate (TEOS), is then conformally deposited over the array of vertical columns, each capped with the low work function material, to form a covered structure. The covered structures are then facet etched to form an array of low work function material-tipped field emission tips. Redeposition material generated by the facet etch, comprising a mixture of material from the vertical column, the low work function material, and the sacrificial material, collects in exposed corners of the sacrificial material at a junction of the vertical column and the conductive substrate during the facet etch. Although such redeposition material would be difficult to remove if deposited directly on the conductive material of the tips and underlying substrate, the presence of the sacrificial material under the redeposition material allows the redeposition material to be easily removed using a clean-up technique, such as a hydrofluoric acid (HF) dip or a diluted HF dip, as known in the art. The mask element is then removed, as known in the art.
Thus, the present invention allows for easy incorporation of a variety of materials on top of the field emission tips to improve their performance.
While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention can be more readily ascertained from the following description of the invention when read in conjunction with the accompanying drawings, in which:
As shown in
As shown in
An etch mask material is patterned to define etch mask element 104 on the low work function material 112, as shown in
Having thus described in detail preferred embodiments of the present invention, it is to be understood that the invention defined by the appended claims is not to be limited by particular details set forth in the above description as many apparent variations thereof are possible without departing from the spirit or scope thereof.
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|Clasificación de EE.UU.||313/336, 313/495, 313/351, 313/311, 313/309|
|Clasificación internacional||H01J1/02, H01J1/304|
|Clasificación cooperativa||H01J1/3044, H01J2201/30446, H01J1/304, H01J31/127|
|Clasificación europea||H01J1/304, H01J31/12F4D, H01J1/304B2|
|4 Ene 2010||AS||Assignment|
Owner name: ROUND ROCK RESEARCH, LLC,NEW YORK
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Effective date: 20091223
Owner name: ROUND ROCK RESEARCH, LLC, NEW YORK
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:MICRON TECHNOLOGY, INC.;REEL/FRAME:023786/0416
Effective date: 20091223
|14 Ene 2010||FPAY||Fee payment|
Year of fee payment: 4
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Year of fee payment: 8